cmd/go: fix TestNewReleaseRebuildsStalePackagesInGOPATH for runtime move
CL 600436 moved runtime/internal/sys to internal/runtime/sys and updated
TestNewReleaseRebuildsStalePackagesInGOPATH in part accordingly. This is
the other part that's needed for it to pass.
For #65355.
Change-Id: I26cff96c15caf185a4ee2c8fb31ec6c877ab87e2
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest
Reviewed-on: https://go-review.googlesource.com/c/go/+/600595 Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: David Chase <drchase@google.com>